1. Field of the Invention
The present invention relates to high-frequency transmission-lines, and more particularly relates to a transmission-line having a line transition device between a dielectric waveguide and a waveguide. Moreover, the invention relates to a primary radiator, an oscillator, and a transmitter which use a line transition device.
2. Description of the Related Art
Dielectric waveguides and waveguides. have been used as transmission lines for high frequencies, such as the microwave band, and the millimeter wave band. A typical example of a dielectric waveguide is a non-radiative dielectric (NRD) waveguide. A typical example of a waveguide is a hollow tube through which microwave electromagnetic radiation can be transmitted with relatively slight attenuation. Waveguides often have a rectangular cross section, but some have a circular cross section.
A line transition device between a dielectric waveguide and a waveguide is disclosed, for example, in Japanese Laid-open Patent Application No. 8-70205, which corresponds to U.S. Pat. No. 5,724,013, in which the line transition device between the dielectric waveguide and the waveguide is constructed by tapering an edge of a dielectric strip of the dielectric waveguide and expanding an edge of the waveguide into a horn-shape. The cross-sectional shape of the waveguide used for a line transition is normally rectangular. Line transition devices using a waveguide having a circular cross section are used infrequently.
However, the end face of the dielectric strip, and metal parts of the dielectric waveguide and of the waveguide must be shaped into a special form to realize the above-described tapered or horn-shapes. Thus, the transition becomes large. Moreover, such a line transition device is not suitable for changing the propagating direction of a signal because a bend at the transition causes lowering of the transmission efficiency.
In a multi-layered circuit, a structure which causes a dielectric waveguide in each layer to be electromagnetically coupled is disclosed, for example, in Japanese Laid-open Patent Application No. 8-181502. In the application, a through-hole passing through a layer is provided, and an edge of the dielectric waveguide is disposed in proximity to an end of the through-hole, whereby both dielectric waveguides are electromagnetically coupled through the through-hole.
This structure requires a reflector or the like to shield the through-hole, apart from a connection part between the through-hole and the dielectric waveguide, so that a signal propagating from the dielectric waveguide to the through-hole does not leak, which results in a higher cost.
One example of an antenna device using a dielectric waveguide is disclosed in Japanese Laid-open Patent Application No. 8-316727. A dielectric resonator is disposed in the proximity of an edge of the dielectric strip so as to be electromagnetically coupled with the dielectric strip. A high-frequency signal propagating through the dielectric strip is radiated from the dielectric resonator. The dielectric waveguide and the dielectric resonator are disposed between a pair of conductive plates facing each other. A slit is provided in the upper conductive plate adjacent to the dielectric resonator. An electromagnetic wave is radiated from the slit.
However, because the dielectric resonator is used as a primary radiator, it is difficult to expand a frequency band of the antenna.
According to the present invention, a transition device between a dielectric waveguide and a waveguide is constructed by placing a part of a dielectric strip of the dielectric waveguide adjacent to the waveguide, for example, generally perpendicular to the propagating direction of an electromagnetic wave in the waveguide. For even greater electromagnetic coupling, the part of the dielectric strip can advantageously be inserted into the waveguide.
This construction does not employ a construction with radiation from the end of the dielectric strip in the direction of the axis, which prevents unnecessary radiation, and which enables line transition converting to be performed with low loss. In addition, since the propagating direction of electromagnetic wave in the dielectric waveguide is perpendicular to that in the waveguide, the degree of freedom in designing a circuit construction is increased and miniaturization of the entire transition device can be achieved.
The above dielectric waveguide may be located between a pair of conductive plates facing each other. By unifying a part of the pair of conductive plates and an end of the waveguide, it is easy to obtain matching between the dielectric waveguide and the waveguide. Alternatively, in the transition device between the dielectric waveguide and the waveguide, by locally changing the shape of a cross section of the waveguide, it is easy to obtain matching between both the dielectric waveguide and the waveguide.
By placing multiple dielectric waveguides inserted into or adjacent to the waveguide, the dielectric waveguides are electromagnetically coupled through the waveguide. By appropriately selecting location positions, a transmission signal can be transmitted in an arbitrary direction. By appropriately selecting the length of the waveguide, in a multiple layer circuit, dielectric waveguides in different layers can be mutually electromagnetically coupled.
In the above transition device, by opening one end of the waveguide, the waveguide having the opening at the end thereof functions as a primary radiator. A signal is propagated through the dielectric waveguide and is radiated through the waveguide. Since the waveguide is used as a radiator, a broadband antenna device can be realized.
An oscillator of the present invention includes an oscillating element in the waveguide and a coupling conductor. The oscillating output signal is transmitted from the oscillating element and is electromagnetically coupled with the coupling conductor in a resonance mode of the waveguide. This construction allows the oscillating output signal to be converted into a signal in the transmission mode of the dielectric waveguide through the resonance mode of the waveguide. These constructions enable the oscillating signal to be easily transmitted through the dielectric waveguide.
A transmitter of the present invention includes the dielectric waveguide, an antenna device having the primary radiator employing the waveguide, and an oscillator generating a transmission signal to the antenna device. Alternatively, the transmitter includes the dielectric waveguide, the oscillator employing the waveguide, and the antenna device transmitting the output signal from the oscillator. With above these constructions, the transmitter having small size, low loss, and a broad band can be obtained.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings.